1. Field of the Invention
The present invention relates to a system for the prevention of contact between the analyzing head and transparent drum of a color scanner of the rotary drum scanning type, especially a color scanner which is selectively adapted with transparent drums of different diameters for differing scales of the reproduction.
2. Description of the Prior Art
A scanner system for a color scanner of the above-mentioned type is essentially provided with a transparent drum, an analyzing head, a main scanning driver, and a subscanning driver. The transparent drum is made from a colorless transparent material and the color original is held thereon. The drum is rotatable in a main scanning direction by the main scanning driver. The analyzing head is movable relative to the transparent drum by the subscanning driver. The subscanning direction is transverse to the direction of rotation of the transparent drum. A threaded shaft or screw may be used to couple the subscanning driver to the analyzing head. In such a color scanner, a plurality of transparent drums having different diameters are provided. One of them is chosen for use in the color scanner in accordance with the desired reproduction scale.
The reproduction scale required for such a color scanner extends from 50% to 1600%, and each transparent drum is used to cover from a half scale to a double scale of its standard scale. For example, if four transparent drums having 100%, 200%, 400% and 800% standard scales respectively are prepared for reproduction, it is possible to cover the full range of desired scales by respectively giving them ranges of reproductive scales overlapping with each other, i.e., from 50% to 200% reproductive scales for the drum having a 100% standard scale, from 100% to 400% reproductive scales for the drum having a 200% standard scale, from 200% to 800% reproductive scales for the drum having a 400% standard scale, and from 400% to 1600% reproductive scales for the drum having a 800% standard scale.
The four standard scales described above are generally obtained by choosing the ratio of drum diameters among the four different drums to be R, R/2, R/4 and R/8, in inverse proportion to their standard scales.
The analyzing head is comprised of a light-emitting device and color detector which are assembled in a body and mounted on a carrier. The light-emitting device and color detector are moved in a direction generally perpendicular to the cylindrical surface of the transparent drum in order to suit the different diameters of the various transparent drums which may be used in the color scanner. The light-emitting device and color scanner are positioned at one of a predetermined number of positions.
The subscanning drive system for moving the analyzing head along the length of the transparent drum is usually comprised of a threaded shaft or screw to which the carrier is connected by a pair of half-nuts provided at the side of the carrier. The carrier is movably mounted on a pair of rails so that the analyzing head may be moved smoothly at a predetermined speed on the rails for scanning.
In a scanner of the rotary drum scanning type, transparent drums of differing diameters are used, one at a time. To change drums, the analyzing head may be moved to one side by its driving motor, and one transparent drum may be changed for another. The operator is required to adjust the position of the analyzing head to one of the predetermined positions previously mentioned. However, the operator sometimes forgets to make such an adjustment. In this situation, the analyzing head may possibly contact the transparent drum, with a catastrophic effect on the scanner, which requires very high accuracy. For the prevention of such an accident, the operator has to take such prudent care that the operating efficiency of the scanner as a whole is impaired.